The present invention relates, generally, to image processing apparatuses, image processing methods, recording media and programs, and more particularly, to an image processing apparatus, an image processing method, a recording medium, and a program capable of monitoring a surveillance area in a stable manner.
Security systems (surveillance apparatuses) for determining whether an invader has entered a predetermined area have been increasingly used.
As conventional security systems or invasion detection apparatuses, a combination of an image capturing apparatus and an image processing apparatus, or a detection apparatus which detects the temperature of a human body by using a pyroelectric sensor or the like, has been proposed.
Alternatively, as disclosed in Japanese Unexamined Patent Application Publication No. Hei-10-232985, for example, an apparatus has been proposed which projects spots divided into a two-dimensional grid pattern, and captures a projection image at a predetermined cycle to monitor the position and posture of a person from a change in the coordinates of each spot.
Further, as disclosed in Japanese Unexamined Patent Application Publication No. Hei-11-225326, for example, an apparatus has been proposed which emits an optical pattern to obtain a range image, detects the motion of an object and records a two-dimensional image obtained when the motion is detected, in a predetermined recording medium.
Furthermore, as disclosed in Japanese Unexamined Patent Application Publication No. Hei-7-129781, for example, an apparatus has been proposed which is provided with a sensing system that extracts change information from continuous motion images in a non-contact and remote manner without using a special illumination and light-emitting apparatus, and drives a subsequent processing system, if necessary.
When an image capturing apparatus and an image processing apparatus are combined, they specifically operate in the following way. As shown in FIG. 1, a surveillance area 2, which includes an object 1 under surveillance, is specified. The image capturing apparatus stores the brightness of the surveillance area 2 which is in a normal state (has no invading object), and has it as a reference image. The image processing apparatus successively captures images to detect a change in the brightness of the surveillance area 2, compares them with the reference image, detects, for example, a large difference in brightness caused by the shadow 11a of an invading object 11, as shown in FIG. 2, and determines that something has occurred (the invading object has been detected).
In this method, however, if the surrounding brightness is changed during image capturing, it can be assumed that the brightness of the surveillance area 2 is changed from that obtained before, and the reference image cannot be used as a reference any more.
When the brightness is changed in time by the flicker of a fluorescent light 3 as shown in FIG. 3, for example, if the shadow 11a is generated by the invading object 11 at a moment when the brightness is increased, a reduction in brightness caused by the shadow 11a is not as large as expected, and it may be not determined that something has occurred.
When an incandescent lamp 4 disposed close to the surveillance area 2 is turned on as shown in FIG. 4, the brightness of the surveillance area 2 is increased. If the shadow 11a is generated by the invading object 11, a reduction in brightness caused by the shadow 11a is not as large as expected, and it may be not determined that something has occurred.
To prevent these erroneous operations, when it is determined that the brightness of the entire system has been changed, it is necessary to store the reference image again, which is troublesome work.
When a charge-coupled-device (CCD) camera is used, for example, since image capturing is performed at an interval of 30 Hz (that is, it takes 33 ms to capture a one-frame image), if the invading object 11 moves fast across the surveillance area 2, the shadow 11a of the invading object 11 cannot be detected.
Further, when an apparatus provided with a pyroelectric sensor is used, since it responds to any objects emitting heat, including small animals such as dogs and cats in addition to persons, erroneous operations frequently occur.
There is also another method in which an infrared light source and a sensor for receiving infrared light are installed at an invasion path, and invasion is detected when the invading object 11 blocks off the light emitted from the light source to the sensor. To detect invasion at a wide area, it is necessary to install a great number of such apparatuses, which increases the cost and the size of the system.